<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 标签选择器 */
        div{
            font-size: 20px;
        }
        /* 类选择器 */
        .btn{
            background-color: #ccc;
            width: 80px;
        }
        /* id选择器 */
        #span-bgc{
            background-color: orange;
        }
        /* 后代选择器 */
        .container .title{
            font-size:50px ;
            background-color: blue;
        }
        /* 后代选择器——子元素 */
        .container>.title{
            background-color: red;
        }
        
        /* 伪类选择器 */
        .btn:hover{
            background-color: orange;
        }
        .btn:active{
            background-color: red;
        }
    </style>
</head>
<body>
    <div>
        aaaaa
    </div>
    <div class="container">
        11111
        <div>
            <span class="title">1111</span>
        </div>
        <span class="title">2222</span>
        <span class="title" id="span-bgc">3333</span>
    </div>
        
    </div>
    <button class="btn">按钮</button>
</body>
</html>